In government, municipal, and law enforcement applications, there is sometimes a desire to track a communications device. Since it is not uncommon for a person to carry a cellular telephone device with them on a daily basis, there may be desire by local police and fire departments to use a corresponding cellular telephone device to help locate a missing person, for example, a person trapped in a collapsed building or a fugitive. Of course, in these applications, such as tracking a cellular communications device, the device and associated user are not actively attempting to mask their location, i.e. an uncooperative communications device. Conventional approaches to communications device location include systems comprising a plurality of sensors. These systems typically use a triangulation method to determine the location of the communications device.
One approach to communications device location, for example, a cellular telephone device, is disclosed by U.S. Pat. No. 6,407,703 to Minter et al. The system of Minter et al. includes a plurality of sensors situated in multiple locations/platforms. The system uses angle of arrival (AOA), time difference of arrival (TDOA), and terrain altitude information from signal intercepts from the cellular telephone device to determine the location thereof. The sensors use accurate time synchronization for determining the TDOA of the intercepted signals.
Another approach is disclosed in U.S. Pat. No. 5,719,584 to Otto, assigned to the present application's assignee, Harris Corporation of Melbourne, Fla. This system uses a plurality of ground based sensors to determine a location of the cellular telephone device by measuring TDOA and AOA values. This network of sensors is also synchronized.
Another approach is disclosed in U.S. Patent Application Publication No. 2004/0135717 to Gounalis. Gounalis discloses a system for detecting wireless transmission signals from an emitter. The system determines and implements a selective scanning strategy, for example, using a frequency domain windowing approach.
Another approach is disclosed in U.S. Pat. No. 7,944,468 to Hoffman et al. Hoffman et al. discloses a predictive threat detection system. The system includes a sensor network spread over an urban environment, and combines data for analysis from each of these sites. A potential drawback to the above systems is that no approach provides a method for distributing information to cooperative communications devices. Moreover, deploying a large network of sensors, such as in Hoffman et al., can be expensive and impractical.